The invention relates to a vibration damper with adjustable damping force.
DE 10 2004 054 474 B3 describes a vibration damper with adjustable damping force, comprising a piston rod, which is installed together with a piston with freedom of axial movement in a cylinder filled with damping medium, wherein the piston divides the cylinder into a working space on the side of the piston rod and a working space on the side away from the piston rod. The vibration damper further comprises an adjustable damping valve, which is connected to at least one of the two working spaces by a fluid connection. Another damping valve which moves in the closing direction as a function of the flow velocity of the damping medium is connected in series, relative to the flow of the damping medium, to the adjustable damping valve. A pressure-limiting valve in the form of a bottom valve is connected hydraulically in parallel to the adjustable damping valve. In this design, it has been observed that the action of the damping valve which acts as a function of the flow velocity of the damping medium is also dependent on the adjustable damping valve installed downstream. When the piston rod travels inward and the flow through the adjustable damping valve is at its maximum, the velocity-dependent damping valve can assume a throttling position relative to the parallel bottom valve even at a relatively slow inward travel velocity. After the closing, the volume flow rate through the bottom valve would then be correspondingly greater. If, however, the adjustable damping valve assumes an operating position with a strong damping force and throttling action, the velocity-dependent damping valve can be in a state in which it exerts almost no effect at all. This effect becomes more obvious when the adjustable damping valve is imagined as a valve which can be completely blocked. In this case, there would be no volume flow rate at all through the velocity-dependent damping valve either. This dependence between the adjustable damping valve, the pressure-limiting valve or bottom valve, and the velocity-dependent damping valve determines the point at which the velocity-dependent damping valve goes into action. It is therefore very difficult to determine the closing behavior of the velocity-dependent damping valve.